Ramsey County is a county in the U.S. state of Minnesota. As of the 2020 census, the population was 552,352, making it the state's second-most populous county, and was estimated to be 542,015 in 2024. Its county seat and largest city is Saint Paul, the state capital and the twin city of Minneapolis. The county was founded in 1849 and is named for Alexander Ramsey, the first governor of the Minnesota Territory. Ramsey County is part of the Minneapolis–Saint Paul–Bloomington, MN–WI Metropolitan statistical area. It is Minnesota's smallest and most densely populated county, as well as the 38th-most densely populated county in the United States in 2010.

With the establishment of the Minnesota Territory in 1849, nine counties, including Ramsey County, were created. In 1849, Ramsey County included all of what later became the present-day counties of Ramsey, Anoka, Isanti, and Kanabec, as well as parts of Washington, Pine, Carlton, Aitkin, Mille Lacs, and Hennepin. One of Ramsey County's early settlers was Heman Gibbs, whose farm is now the Gibbs Museum of Pioneer and Dakotah Life (Gibbs Farm) in Falcon Heights. Ramsey County remained largely farmland until small villages began to appear in the late 19th century, with the incorporation of North St. Paul in 1887, New Brighton in 1891, and White Bear Lake in 1921.

Ramsey County is overwhelmingly Democratic in presidential elections, not having voted for a Republican presidential nominee since 1924. In 2020, Democratic nominee Joe Biden received the largest share of the vote for any candidate in the county's history, with over 71%.

The Ramsey County Sheriff's Office was established in the old Minnesota Territory in 1849. The current sheriff is Bob Fletcher, who was elected in 2018 and reelected in 2022. The Ramsey County sheriff is elected to a four-year term in an election concurrent with the federal midterm elections.

The sheriff's office provides patrol and investigation for communities without local police forces and is available as backup for all communities. In addition to enforcing the law, the office provides town police services under contract to Arden Hills, Falcon Heights, Little Canada, North Oaks, Shoreview, Vadnais Heights, and White Bear Township.

The Ramsey County Sheriff's Office provides a number of unique services as mandated by law. This includes detention for court and other court services, safety, rescue, and law enforcement on the waterways. The office provides safety classes and coordinates community volunteer efforts. It is responsible for the county jail, more officially the Adult Detention Center, which can hold 500 prisoners and has a staff of about 150.

The Ramsey County attorney prosecutes felony crimes committed within the jurisdiction of Ramsey County. The current county attorney is John Choi, who was elected in 2010 and reelected in 2014, 2018, and 2022.

The county commission elects a chair who presides at meetings. Commissioners as of February 24, 2025, are: